This invention relates to a heat-sensitive record material and particularly to a heat-sensitive record material which is superior in adaptability to high speed recording and retainability of the recorded images.
There are known heat-sensitive record materials utilizing the colorforming reaction between a basic colorless chromogenic material and an electron accepting acidic reactant material (hereinafter referred to as "acceptor"), in which color images are produced by heating to contact with each other of the basic colorless chromogenic material and the acceptor. Since the heat-sensitive record materials are relatively economical and the recording machine is compact and relatively easily maintained, they are useful as a recording medium for various field, such as facsimiles, electronic computers and telex machines.
As the applied fields are broader, the required properties are increased. Recently, the heat-sensitive record materials are required not only to be superior in adaptability to high speed recording but also to be superior in stability of the recorded images at high temperature and high humidity and fogging-free in the white area (non-recorded area) at high temperature and high humidity.
There are proposed heat-sensitive record materials comprising various additive to improve the retainability of the recorded images. However, since a sufficient improvement is not obtained or a new problem occurs with the improvement, the desired results can not be always obtained.
For example, U.S. Pat. No. 4,473,831 discloses 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane as such additive. However, using the additive, heat-sensitive record materials in which the white area is stably maintained to be fogging-free at high temperature can not be obtained.
The object of the invention is to provide heat-sensitive record materials superior in not only adaptability to high speed recording but also stability of the recorded images at high temperature and high humidity and further in which the white area is maintained to be fogging-free at high temperature and high humidity.